This application claims the benefit of German patent application number 10 2013 102 069.0 filed on Mar. 1, 2013, which is incorporated herein by reference in its entirety and for all purposes.
The invention relates to a proportional directional control valve for controlling a hydraulic consumer, in particular for use in a hydropneumatic suspension system, comprising a housing that has a pressure port for feeding pressurized hydraulic fluid from a pressure medium source, a tank port for discharging hydraulic fluid to a reservoir, and a first and a second working port for connecting to the hydraulic consumer, and comprising a control element that is movably held in the housing, and an actuator for moving the control element, it being possible by means of the control element, in dependence on the position thereof relative to the housing, to enable different flow paths between the working ports and the pressure port and tank port, and the flow cross-sections of the flow paths being continuously variable in dependence on the adjustment travel of the control element.
The invention further relates to a hydraulic circuit comprising a hydraulic cylinder that has a cylinder body, in the interior of which a piston that delimits a piston chamber is disposed, and comprising a proportional directional control valve of the aforementioned kind.
In addition, the invention relates to a hydropneumatic suspension system for variable suspension loads, comprising a proportional directional control valve as described above.
In hydraulics, proportional directional control valves are used to enable or block the path for the hydraulic fluid or to change the flow direction of the hydraulic fluid. The directional control valves comprise a movable control element which, depending on its position, enables different flow paths. The flow cross-sections of the flow paths are changeable in a continuously variable manner, depending on the adjustment travel of the control element. In order for the adjustment travel not to be influenced by pressures of the hydraulic fluid which occur, the control element is configured in such a manner that the pressure forces acting on the control element in the direction of movement and counter to the direction of movement of the control element, in particular the pressure forces acting on the end faces of the control element, cancel each other out. By means of such proportional directional control valves, hydraulic consumers can be controlled, and in particular the movement of a hydraulic cylinder that has a cylinder body, in the interior of which a piston having a piston rod which protrudes from the cylinder body is disposed, can be controlled. Such hydraulic cylinders are used, for example, in hydropneumatic suspension systems that are used in particular in vehicles with variable suspension loads, for example, tractors with receiving means for attachments.
In hydropneumatic suspension systems, a hydraulic cylinder is disposed between spring-loaded and nonspring-loaded masses of the vehicle. The hydraulic cylinder comprises a piston chamber which is connected to a hydraulic accumulator and which can be acted on by pressurized hydraulic fluid, and which carries the suspension load. Moreover, the hydraulic cylinder has an annular chamber that sealingly encloses the piston rod of the hydraulic cylinder.
With increasing suspension load, hydraulic fluid is pushed out of the piston chamber into the first hydraulic accumulator so that the relative position of the spring-loaded and nonspring-loaded masses changes. The change in the relative position is detected by sensors that are connected to an electrical control unit. The electrical control unit controls a valve device in such a manner that the valve device changes its switching position and thereby feeds pressurized hydraulic fluid to the piston chamber until a predefined relative position is again reached. With decreasing suspension load, hydraulic fluid flows out of the hydraulic accumulator into the piston chamber so that the relative position of the spring-loaded and nonspring-loaded masses changes again. The change in the relative position is detected again, so that the valve device changes its switching position again and hydraulic fluid can flow out of the piston chamber.
Such valve devices for hydropneumatic suspension systems usually have either two directional control valves, each having an electromagnet as an actuator and each having two switching positions, or a single directional control valve having two electromagnets and three switching positions. A hydropneumatic suspension system having two directional control valves is known from the publication DE 101 07 631 A1. The two directional control valves each comprise a magnetic coil by means of which a control element in a housing can be moved between a first switching position and a second switching position against a resiliently elastic restoring force.
The publication DE 197 19 076 A1 describes a hydropneumatic suspension system in which a single directional control valve is provided, the control element of which can be moved from a central neutral position, in which all working ports are connected to the tank port, into a working position by activating a magnetic coil in each case. In a first working position, which, starting from the neutral position, can be reached by moving in a first actuating direction, one of the two working ports is connected to the tank port and the other working port is connected to the pressure port. In a second working position, which can be assumed by the control element by moving in a second actuating direction that is opposite to the first actuating direction, both working ports are connected to the pressure port.